Magnetic disks and disk drives are conventionally employed for storing data in magnetizable form. Preferably, one or more disks are rotated on a central axis in combination with data transducing heads positioned in close proximity to the recording surfaces of the disks and moved generally radially with respect thereto. Magnetic disks are usually housed in a magnetic disk unit in a stationary state with a magnetic head having a specific load elastically in contact with and pressed against the surface of the disk. Data are written onto and read from a rapidly rotating recording disk by means of a magnetic head transducer assembly that flies closely over the surface of the disk. Preferably, each face of each disk will have its own independent head.
Disc drives at their most basic level work on the same mechanical principles as media such as compact discs or even records, however, magnetic disc drives can write and read information much more quickly than compact discs (or records for that matter!). The specific data is placed on a rotating platter and information is then read or written via a head that moves across the platter as it spins. Records do this in an analog fashion where the disc's grooves pick up various vibrations that then translate to audio signals, and compact discs use a laser to pick up and write information optically.
In a magnetic disc drive, however, digital information (expressed as combinations of “0's” and “1's”) is written on tiny magnetic bits (which themselves are made up of many even smaller grains). When a bit is written, a magnetic field produced by the disc drive's head orients the bit's magnetization in a particular direction, corresponding to either a 0 or 1. The magnetism in the head in essence “flips” the magnetization in the bit between two stable orientations. In currently produced hard disc drives, longitudinal recording is used. In longitudinal recording, the magnetization in the bits is flipped between lying parallel and anti-parallel to the direction in which the head is moving relative to the disc.
Increasing areal densities within disc drives is no small task. For the past few years, technologists have been increasing areal densities in longitudinal recording at a rate in excess of 100% per year. But it is becoming more challenging to increase areal densities, and this rate is expected to eventually slow until new magnetic recording methods are developed.
To continue pushing areal densities in longitudinal recording and increase overall storage capacity, the data bits must be made smaller and put closer together. However, there are limits to how small the bits may be made. If the bit becomes too small, the magnetic energy holding the bit in place may become so small that thermal energy may cause it to demagnetize over time. This phenomenon is known as superparamagnetism. To avoid superparamagnetic effects, disc media manufacturers have been increasing the coercivity (the “field” required to write a bit) of the disc. However, the fields that can be applied are limited by the magnetic materials from which the head is made, and these limits are being approached.
Newer longitudinal recording methods could allow beyond 140 gigabits per square inch in density. A great challenge however is maintaining a strong signal-to-noise ratio for the bits recorded on the media. When the bit size is reduced, the signal-to-noise ratio is decreased, making the bits more difficult to detect, as well as more difficult to maintain stable recorded information.
Perpendicular recording could enable one to record bits at a higher density than longitudinal recording, because it can produce higher magnetic fields in the recording medium. In perpendicular recording, the magnetization of the disc, instead of lying in the disc's plane as it does in longitudinal recording, stands on end perpendicular to the plane of the disc. The bits are then represented as regions of upward or downward directed magnetization (corresponding to the 1's and 0's of the digital data).
A disk recording medium is shown in FIG. 1. Even though FIG. 1 shows one side of the non-magnetic disk, magnetic recording layers are sputter deposited on both sides of the non-magnetic aluminum substrate of FIG. 1. FIG. 1 shows a cross section of a disc showing the difference between longitudinal and perpendicular recording.
Perpendicular recording still has other unsolved problems. On the other hand, longitudinal recording still has room left before reaching the superparamagnetic limit. Thus in recent years, considerable effort has been expended to achieve higher areal recording density using longitudinal recording. Ever increasing hard disk drive areal recording density requires continuously aggressive media signal to noise ratio (SNR) enhancement. One way for creating in a high density magnetic recording with a high signal to noise ratio (SNR) is by enhancing the media Mrt oriented ratio (OR). Media on textured aluminum substrates can achieve Mrt OR higher than 1.8. However, it has been a great challenge to obtain even Mrt OR of about 1.3 on textured glass substrates. This invention provides a solution to satisfy this long-standing need of increasing the Mrt OR of recording media on textured glass substrate beyond about 1.3.